The objectives of this project are to determine how 2450 MHz microwave radiation interacts with biological material at the cellular and subcellular level, to observe any effects of this interaction, and to relate the amount of microwave energy absorbed to the effect. The biological specimens include mitochondria cardiac cells, lysosomes, and cellular enzymes. For these experiments, a waveguide exposure apparatus has been used which can maintain the specimens at physiologic temperatures (about 37C) at specific absorption rates up to 100 mW/g. No effects were noted on in vitro activity of creatine phosphokinase and acetylcholinesterase at SAR's up to 50 mW/g. Embryonic cardiac cells obtained from 9-day old quail, exhibited an increase in cell membrane permeability to trypan blue at SAR's of 10, 50 and 100 mW/g, following 90 minutes exposure. Cellular damage was noted at an SAR of 100 mW/g. Methods for examining the influence of microwave radiation on mitochondria have been developed. Preliminary results indicate the respiratory control ratio of mitochondria may be altered by in vitro microwave exposure (100 mW/g).